The present invention relates to an electro-optical apparatus for inspecting a printed-circuit board with circuit components or units mounted thereon to determine whether each component is properly soldered on the printed-circuit board.
Inspection of the presence of a fault such as misalignment, detachment, or floating of any circuit component mounted to soldering on a printed-circuit board is conventionally performed by human eyes. Advanced compacting and weight-reducing technologies rapidly promote the tendency toward a highly dense mounting of compact circuit components on a printed-circuit board. Under these circumstances, it is almost practically impossible to perform a visual inspection of the densely mounted small components for a long period of time without making errors such as the fatigue-induced errors made by human inspectors. Accordingly, there has been a need for automatic inspection systems. One such automatic inspection system proposed heretofore is disclosed in U.S. Pat. No. 4,642,813. The disclosed system is so constructed as to inspect the positional displacement or misalignment of components by using two-dimensional images of the respective components.
Since the automatic inspection system thus constructed uses two-dimensional information on an image of each component recorded by a video camera, it is difficult to detect such a fault occurring when a component as a whole or a lead of an IC device is soldered onto a printed-circuit board in floating condition.